KR20050033839A - Radiographic apparatus and radiation detection signal processing method - Google Patents

Abstract

A radiographic apparatus and a method for processing radiation detection signals are provided to remove a time delay component from the radiation detection signals by using a time delay remover performing recursive calculations. A radiographic apparatus includes a radiation emitting device(1) for emitting X rays toward a patient(M), a radiation detector(2) for detecting X rays transmitted through the patient(M), a signal sampling device(3) for digitizing X-ray detection signals taken from the radiation detector(2) at predetermined sampling time intervals, a detection signal processor(4) for creating X-ray images based on X-ray detection signals outputted from the signal sampling device(3), and an image monitor(5) for displaying the X-ray images created by the detection signal processor(4). The radiation emitting device(1) and the radiation detector(2) are opposed to each other across the patient(M). During a radiography process, the radiation emitting device(1) is controlled by an emission controller(6) to emit X rays in a form of a cone beam to the patient(M). A time delay remover(10) performs recursive calculations according to predetermined mathematical expressions to remove time delay components from detected radiographic signals.

Description

Radiation imaging device and radiation detection signal processing method {RADIOGRAPHIC APPARATUS AND RADIATION DETECTION SIGNAL PROCESSING METHOD}

According to the present invention, the radiation detection signal is extracted from the radiation detection means by the signal sampling means at a predetermined sampling time interval in accordance with the irradiation of the radiation by the radiation irradiation means, and at the same time, a radiation image is obtained based on the extracted radiation detection signal. The present invention relates to a radiation imaging apparatus and a radiation detection signal processing method for medical or industrial use, and more particularly, a technique for removing a time delay of a radiation detection signal due to the radiation detection means from the radiation detection signal extracted from the radiation detection means. It is about.

In the medical X-ray fluoroscopy apparatus which is one of the representative apparatuses of the radiation imaging apparatus, the X-ray detector which detects the X-ray transmission image of the inspected object produced | generated recently by the X-ray irradiation by an X-ray tube, is extremely used using a semiconductor etc. A flat panel type X-ray detector (hereinafter referred to as "FPD" as appropriate) in which many X-ray detection elements are arranged vertically and horizontally on the X-ray detection surface is used.

That is, in the X-ray fluoroscopy apparatus, an X-ray detection signal for one X-ray image is extracted from the FPD at sampling time intervals in accordance with the irradiation of the X-ray tube to the subject under investigation. On the basis of the X-ray detection signal, an X-ray perspective imaging apparatus is constructed so as to obtain an X-ray image corresponding to the X-ray transmission image of the subject at each sampling time interval. When FPD is used, it is advantageous in terms of device structure and image processing because it is light in weight and does not generate complex detection distortion compared with conventionally used image intensifiers and the like.

However, when FPD is used, there is a problem that adverse effects due to time delay due to FPD appear on the X-ray image. Specifically, when the sampling time interval for extracting the X-ray detection signal from the FPD is short, the remainder of the signal whose extraction is not broken is applied to the next X-ray detection signal as a time delay. Therefore, when an X-ray detection signal of one image is extracted from the FPD at 30 sampling time intervals for one second, and an X-ray image is created to display a moving image, the time delay appears as an afterimage on the screen. As a result of overlapping of images, problems such as blurring of moving images occur.

In the case of acquiring a computer tomography image (CT image), in the case of acquiring a computer tomographic image (CT image), a time delay is calculated from a radiation detection signal extracted from the FPD at a sampling time interval Δt. A technique for removing is proposed.

In other words, the United States, the patent specification, as by a time delay minutes included in each of the radiation detection signal extracted by the sampling time interval of the impulse response which is the time delay minutes consists of several exponential function, the time delay of data from the radiation detection signal y _k An arithmetic processing to remove the delay removal radiation detection signal x _k is performed by the following equation.

Δt: Sampling time interval

     k: subscript representing the kth point in time in the sampled time series

     N: Number of exponential functions with different time constants that make up the impulse response

     n: subscript representing one of the exponential functions that make up the impulse response

: Strength of exponential function n

: Decay time constant of exponential function n

However, when the inventors apply the arithmetic processing technique proposed by the above-mentioned US patent specification, the artifacts due to the time delay are not avoided, and only the result that a certain X-ray image can not be obtained is obtained. It was confirmed that the time delay was not resolved.

In addition, regarding the time delay problem of FPD, US Patent No. 5517544 calculates the time delay from the X-ray detection signal by approximating the time delay of the FPD with one exponential function in the case of acquiring a CT image. A technique for removing by treatment has been proposed. However, as a result of the inventors intensively examining the arithmetic processing technique proposed by the above-mentioned US patent specification, it has been found that it is unreasonable to approximate the time delay portion of the FPD by one exponential function, and the time delay of the FPD is not solved. .

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a radiation imaging apparatus and a radiation detection signal processing method capable of accurately removing a time delay of a radiation detection signal due to the radiation detection means from the radiation detection signal extracted by the radiation detection means. It aims to provide.

In order to sufficiently eliminate the time delay of the FPD, the following method is considered. According to this method, the time delay caused by the impulse response of the FPD is eliminated specifically with respect to the time delay of the FPD by the following recursive equations A to C.

Δt: Sampling time interval

     k: subscript representing the kth point in time in the sampled time series

Y _k : the radiation detection signal extracted at the kth sampling time point

X _k : Radiation detection signal after correction removing time delay from Y _k

X _k-1 : X _k before 1

S _{n (k-1)} : S _nk before 1

     exp: exponential function

     N: Number of exponential functions with different time constants constituting the impulse response

     n: subscript representing one of the exponential functions that make up the impulse response

: Strength of exponential function n

: Decay time constant of exponential function n

when k = 0 X ₀ = 0, S _n0 = 0

However, in solving the time delay of the FPD proposed in the previous method, the time delay of the FPD can be solved to a considerable extent, but it does not reach the accurate resolution of the time delay of the FPD. So, to further improve, the inventors continued to review.

In the recursive operation proposed in the previous method, N, which is an impulse response coefficient that defines a condition related to an impulse response, , Is obtained in advance and the radiation detection signal Y _k is applied to the equations A to C in the state where it is fixed, and then the radiation detection signal X _k is calculated after the correction with the time delay removed. In this case, if the radiation detection signal Y _k is the same, the impulse response for the time delay included in the radiation detection signal is also constant.

However, in real FPD, the impulse response of time delay is not constant. The inventors conducted experiments under various conditions on this inconsistent cause and obtained the following findings. In other words, it was found that the impulse response changes when the radiation dose of radiation (for example, X-ray) is different. Fig. 6 is a diagram schematically showing the knowledge, in which the horizontal axis represents the radiation dose W of the radiation and the vertical axis represents the intensity of the exponential function n. Other impulse response coefficients N, It is when we made constant. As shown in Fig. 6, the intensity of the exponential function when the radiation dose of radiation is changed I know that changes correspondingly.

In addition, If N is constant and the radiation dose of radiation changes, Changing too, , N is constant and N is changed when the radiation dose of radiation is changed. Irradiation dose changes frequently according to the shooting conditions, so even with the same FPD, the impulse response coefficients N, , The appropriate value of V will also change frequently. In other words, an appropriate value of the impulse response coefficient may be obtained as the radiation dose of radiation changes.

Further, the above-mentioned knowledge is examined and the correspondence between the impulse response coefficient and the irradiation dose, which defines the conditions related to the impulse response in the recursive computation for time delay elimination, is obtained and stored in advance. The impulse response coefficient suitable for the radiation dose to the subject is set in accordance with the correspondence relationship between the impulse response coefficient and the radiation dose. Then, it was reached to obtain a conclusive knowledge that the time delay component can be accurately removed by performing the recursive computation process according to the set impulse response coefficient to remove the time delay component included in each radiation detection signal.

Therefore, this invention based on the said knowledge employs the following structures.

That is, the radiographic image capturing apparatus according to the present invention includes radiation irradiation means for irradiating radiation toward an inspected object, radiation detecting means for detecting radiation transmitted through the inspected object, and sampling a radiation detection signal from the radiation detecting means. A radiographic image capturing apparatus comprising: a signal sampling means for extracting at time intervals and configured to obtain a radiographic image based on a radiation detection signal output at a sampling time interval from the radiation detecting means in response to irradiation with a subject under test; The device includes the following elements:

Time delay that is included in each radiation detection signal extracted at sampling time intervals by impulse response composed of a plurality of exponential functions with different singular or attenuation time constants and is removed from each radiation detection signal by recursive computation. Removal means;

Response coefficient / dose correspondence storage means for storing in advance the correspondence relationship between the impulse response coefficient and the irradiation dose defining a condition related to the impulse response in the recursive computation in the time delay removing means;

An impulse response coefficient setting means for setting an impulse response coefficient appropriate to the radiation dose to the subject under test according to the correspondence relationship between the impulse response coefficient stored in the response coefficient and the dose correspondence relationship storage means and the radiation dose;

The time delay removing means performs recursive calculation processing according to the impulse response coefficient set by the impulse response coefficient setting means to remove the time delay included in each radiation detection signal, and obtains the corrected radiation detection signal.

According to the radiographic image capturing apparatus according to the present invention, the singular or attenuation time constant is a time delay included in the radiation detection signal output from the radiation detection means at a predetermined sampling time interval in accordance with the irradiation line to the inspected object by the radiation irradiation means. As a result of an impulse response composed of a plurality of different exponential functions, when the time delay removing means removes the recursive computation, it is performed as follows. That is, according to the correspondence relationship between the impulse response coefficient and the radiation dose, which define conditions relating to the impulse response in the recursive calculation processing in the time delay elimination means stored in the response coefficient / dose correspondence storage means in advance, The impulse response coefficient setting means sets an impulse response coefficient suitable for the radiation dose to the subject. Then, recursive arithmetic processing is performed in accordance with this set impulse response coefficient, and the time delay included in each radiation detection signal is removed to obtain a radiographic image from the obtained post-correction radiation detection signal.

In this way, when the time delay is removed from the radiation detection signal by the recursive computation processing by the time delay elimination means and the corrected radiation detection signal is calculated, the impulse response in the recursive computation processing for time delay elimination is related. The response coefficient / dose correspondence storage means memorizes in advance the correspondence relationship between the impulse response coefficient and the radiation dose defining the condition, and irradiates the subject under the correspondence relationship between the impulse response coefficient and the radiation dose. Since the impulse response coefficient setting means sets the impulse response coefficient suitable for the dose and the impulse response coefficient for the radiation dose to the subject is set, the recursive computation for time delay removal is performed. The time delay included is accurately eliminated.

Examples of the correspondence relationship between the impulse response coefficient and the irradiation dose described above are as follows.

That is, the response coefficient and dose correspondence relationship storing means is a correspondence relationship between the impulse response coefficient and the radiation dose,

Correlation of Exponential Function as Impulse Response Coefficient with Irradiation Dose,

Correlation between Exponential Function's Attenuation Time Constant and Irradiation Dose as Impulse Response Coefficient,

At least one of the correspondence relationship between the number of exponential functions as the impulse response coefficient and the radiation dose is stored in advance.

In this case, the response coefficient / dose-correspondence relationship storage means stores the correspondence relationship between the intensity of the exponential function as the impulse response and the radiation dose, and the attenuation time constant of the exponential function as the impulse response. Of the intensity of the exponential function, the time constant of the exponential function, and the number of exponential functions according to at least one of the relationship between the abbreviation) and the radiation dose, the number of exponential functions as an impulse response and the radiation dose. At least one is set to a value appropriate to the radiation dose.

In the above-mentioned radiation imaging apparatus,

The time delay removing means is a recursive calculation process for removing the time delay from the radiation detection signal Equation A ~ C,

Δt: Sampling time interval

     k: subscript representing the kth point in time in the sampled time series

Y _k : the radiation detection signal extracted at the kth sampling time point

X _k : Radiation detection signal after correction removing time delay from Y _k

X _k-1 : X _k before 1

S _{n (k-1)} : S _nk before 1

     exp: exponential function

      N: Number of exponential functions with different time constants constituting the impulse response

      n: subscript representing one of the exponential functions that make up the impulse response

: Strength of exponential function n

: Decay time constant of exponential function n

when k = 0 X ₀ = 0, S _n0 = 0

It is preferable to comprise so that it may be performed by.

When the recursive calculation processing to remove the time delay from the radiation detection signal is performed by equations A to C, the radiation detection signal X _k is quickly obtained after correction by removing the time delay by the simple ignition equation of equations A to C. Become.

In addition, an example of the radiation imaging apparatus is a radiation imaging apparatus.

As the impulse response coefficient, including the strength of the exponential function,

The correspondence between the intensity of the exponential function as the impulse response coefficient and the radiation dose is derived based on a plurality of radiation data actually taken under different conditions at the same irradiation time.

In this case, since the correspondence between the intensity of the exponential function as the impulse response coefficient and the radiation dose is the same irradiation time and the radiation dose is derived based on a plurality of radiation data actually photographed at different stages, the exponential function The intensity of the radiation and the radiation dose correspond exactly.

In addition, another example of the radiation imaging apparatus is a radiation imaging apparatus.

As the impulse response coefficient, including the strength of the exponential function,

There are a plurality of exponential functions constituting the impulse response, and the correspondence between the intensity of the exponential function as the impulse response coefficient and the irradiation dose is stored for each exponential function.

In this case, since the impulse response is composed of a plurality of exponential functions, the impulse response is more accurate. In addition, since the correspondence between the intensity of the exponential function as the impulse response coefficient and the X-ray irradiation dose is stored for each exponential function, the intensity of each exponential function can be set more accurately. As a result, the time delay included in each X-ray detection signal is more accurately removed.

In addition, another example of the radiation imaging apparatus is a radiation imaging apparatus.

As the impulse response coefficient, including the strength of the exponential function,

The correspondence between the intensity of the exponential function as the impulse response coefficient and the radiation dose,

only, : Strength of exponential function

     W: radiation dose

    Q: slope of the approximate line representing the relationship between the strength of the exponential function and the radiation dose

    q is expressed as a function of intercepting an approximation line representing the relationship between the intensity of the exponential function and the radiation dose.

In this case, the correspondence between the intensity of the exponential function as the impulse response coefficient and the radiation dose is " Since it is expressed by a simple functional formula, the correspondence between the intensity of the exponential function and the radiation dose can be easily stored.

In addition, the inclination Q of the approximation straight line and the intercept q of the approximation straight line can be obtained as follows. That is, the horizontal axis is scaled in logW, and the vertical axis is Draw a scale with The inclination of the straight line when the graph is plotted as a straight line is the inclination Q of the approximated straight line, and the coordinate on the longitudinal axis of the point where the straight line intersects the longitudinal axis is the intercept q of the approximated straight line.

In the radiation imaging apparatus, an example of the response coefficient and dose correspondence relationship storing means is a table memory for storing the correspondence relationship between the impulse response coefficient and the irradiation dose in a table format.

In this case, the correspondence relationship between the impulse response coefficient and the radiation dose is stored in the table memory in the form of a table, and the impulse response coefficient setting means is stored in the input radiation dose and the response coefficient / dose correspondence storage means. The impulse response coefficient suitable for the input radiation dose is read out and set by matching with the present list.

In the radiation imaging apparatus, an example of the radiation detection means is a flat panel X-ray detector in which a plurality of X-ray detection elements are vertically and horizontally arranged on the X-ray detection surface.

Moreover, the radiation imaging apparatus which concerns on this invention can be applied also to a medical apparatus and an industrial apparatus. One example of the medical apparatus is an X-ray fluoroscopy apparatus, and another example is an X-ray CT apparatus. An example of an industrial apparatus is a nondestructive inspection device.

In addition, the radiation detection signal processing method according to the present invention is a signal for irradiating an object to be detected, extracting the detected radiation detection signal at a predetermined sampling time interval, and obtaining a radiation image based on the radiation detection signal output at the sampling time interval. In the radiation detection signal processing method for performing the process, the method includes the following steps:

Removing the time delay included in each radiation detection signal extracted at a sampling time interval from each radiation detection signal by recursive computation as an impulse response composed of a plurality of exponential functions having different singular or attenuation time constants;

Before the removing step, an impulse suitable for the irradiation dose to the subject under test according to the correspondence between the previously stored impulse response coefficient and the irradiation dose, which defines a condition related to the impulse response in the recursive calculation processing. Setting a response coefficient;

A step of removing the time delay included in each radiation detection signal by performing a recursive calculation process in the removing step according to the impulse response coefficient set in the setting step, and obtaining a corrected radiation detection signal.

According to the radiation detection signal processing method according to the present invention, the radiation imaging apparatus according to the present invention can be preferably implemented.

In the above-described radiation detection signal processing method,

Recursive computations to remove time delays from radiation detection signals

Δt: Sampling time interval

     k: subscript representing the kth point in time in the sampled time series

Y _k : the radiation detection signal extracted at the kth sampling time point

X _k : Radiation detection signal after correction removing time delay from Y _k

X _k-1 : X _k before 1

S _{n (k-1)} : S _nk before 1

     exp: exponential function

      N: Number of exponential functions with different time constants constituting the impulse response

      n: subscript representing one of the exponential functions that make up the impulse response

: Strength of exponential function n

: Decay time constant of exponential function n

when k = 0 X ₀ = 0, S _n0 = 0

It is preferable to perform by.

In the case where the recursive calculation processing for removing the time delay from the radiation detection signal is performed by the formulas A to C, the radiation imaging apparatus in the case of performing this recursive calculation processing by the formulas A to C can be preferably performed. .

In addition, an example of the radiation detection signal processing method is, in the radiation detection signal processing method,

As the impulse response coefficient, including the strength of the exponential function,

The correspondence relationship between the intensity of the exponential function as the impulse response coefficient and the radiation dose is derived based on the plurality of radiation data actually taken under different conditions at the same irradiation time.

When the correspondence relationship is derived based on a plurality of radiation data actually taken under the same step time and the irradiation dose is actually different, the plurality of times the same irradiation time and the irradiation dose is actually taken under the different conditions The radiation imaging apparatus in the case of deriving the corresponding relationship based on the radiation data can be preferably implemented.

In addition, another example of the radiation detection signal processing method is, in the radiation detection signal processing method,

Including an intensity of an exponential function as the impulse response coefficient,

The correspondence between the intensity of the exponential function as the impulse response coefficient and the radiation dose,

only, : Strength of exponential function

    W: radiation dose

   Q: slope of the approximate line representing the relationship between the strength of the exponential function and the radiation dose

   q is expressed as a function of intercepting an approximation line representing the relationship between the intensity of the exponential function and the radiation dose.

In the case where the correspondence is represented by the above formula, the radiation image pickup device when the correspondence is represented by the above equation can be preferably implemented.

One example of the radiation detection signal processing method is to store the correspondence between the impulse response coefficient and the radiation dose in a table memory in the radiation detection signal processing method.

When the correspondence relationship is stored in the table memory in the form of a table, a radiation imaging apparatus can be preferably implemented when the correspondence relationship is stored in the table memory in the form of a table.

In the radiation detection signal processing method, it is preferable to further include a step of previously storing the corresponding relationship between the impulse response coefficient and the radiation dose.

This storing step is performed, for example, at the time of installation of the apparatus or at regular adjustment.

EMBODIMENT OF THE INVENTION Hereinafter, preferred embodiment of this invention is described in detail based on drawing.

First embodiment

1 is a block diagram showing the overall configuration of an X-ray perspective imaging apparatus according to the first embodiment.

As shown in FIG. 1, the X-ray fluoroscopy apparatus detects an X-ray tube (radiation means) 1 for irradiating X-rays toward the subject M and an X-ray that has passed through the subject M. FIG. A / D converter which digitizes and extracts an X-ray detection signal (radiation detection signal) from the FPD 2 (radiation detection means) and the FPD (flat panel type X-ray detector) 2 at a predetermined sampling time interval Δt. (Signal sampling means) 3, a detection signal processing unit 4 for creating an X-ray image based on the X-ray detection signal output from the A / D converter 3, and the detection signal processing unit 4 The image monitor 5 which displays an X-ray image is provided. That is, the X-ray image is acquired based on the X-ray detection signal extracted from the FPD 2 by the A / D converter 3 in accordance with the X-ray irradiation to the subject M, and the obtained X-ray image is imaged. It is a structure projected on the screen of the monitor 5. Hereinafter, the structure of each part of the apparatus of 1st Example is demonstrated concretely.

The X-ray tube 1 and the FPD 2 are disposed to face each other with the subject M interposed therebetween, and the X-ray tube 1 is controlled by the irradiation control unit 6 during X-ray imaging. Irradiating a cone beam X-ray, the transmission X-ray image of the subject M produced | generated by X-ray irradiation is an arrangement relationship projected on the X-ray detection surface of FPD2.

Moreover, while the operator inputs irradiation conditions, such as X-ray irradiation dose, by the operation part 7 etc., the irradiation control part 6 controls the X-ray tube 1 according to the irradiation conditions input by the operation part 7 etc. . For example, in case of continuous X-ray irradiation and single-shot X-ray irradiation, the amount of X-ray irradiation is quite different.

As shown in FIG. 2, in the FPD 2, a large number of X-ray detection elements 2a are placed on the X-ray detection surface on which the transmission X-ray image from the test object M is projected. And vertically and horizontally arranged along the body side direction Y. For example, the X-ray detection elements 2a are vertically and horizontally arranged in a matrix of vertical length 3636 x width 1536 on an X-ray detection surface having a width of about 30 cm x 30 cm. Each X-ray detection element 2a of the FPD 2 has a corresponding relationship with each pixel of the X-ray image created by the detection signal processing section 4, and is detected based on the X-ray detection signal extracted from the FPD 2. An X-ray image corresponding to a transmission X-ray projected on the X-ray detection surface by the signal processing unit 4 is created.

The cross section of the FPD 2 is as shown in FIG. 3. In other words, the semiconductor film 22, which is an X-ray sensitive film (for example, an amorphous Se thick film), in which carriers are generated by the incidence of X-rays, and the bias voltage provided on the surface of the X-ray incidence side of the semiconductor film 22 are applied. Carrier collection electrode 23, part of each X-ray detection element 2a of FPD 2, provided on the X-ray non-incident side of semiconductor film 22, and carrier collection electrode ( It consists of the glass substrate 24 which deposited 23. In the case of the FPD 2, the electric charges collected by the carrier collecting electrode 23 are read by an accumulation / reading electric circuit (not shown) disposed on the glass substrate 24, and at the same time, a current / voltage conversion amplifier of the next stage. (Not shown) and a multiplexer (not shown) to send to the A / D converter 3.

The A / D converter 3 continuously extracts X-ray detection signals for one X-ray image at sampling time intervals Δt, and detects X-rays for creating X-ray images in the detection signal memory section 8 at a later stage. The signal is stored, and the sampling operation (extraction) of the X-ray detection signal is started before the X-ray irradiation. The X-ray image created by the detection signal processing section 4 is sent to the image memory section 9 for holding.

That is, as shown in FIG. 4, at the sampling time interval Δt, all the X-ray detection signals related to the transmission X-ray image at that time point are collected and gradually stored in the detection signal memory section 8. The acquisition start of the X-ray detection signal by the A / D converter 3 before the X-ray irradiation may be performed by a manual operation of an operator, or may be automatically performed in conjunction with an X-ray irradiation instruction operation or the like. It may be.

In addition, as shown in Fig. 1, the X-ray fluoroscopy apparatus of the first embodiment uses a single or attenuation time constant for the time delay included in each X-ray detection signal extracted from the FPD 2 at a sampling time interval Δt. A time delay removal unit (time delay removal means) that calculates an X-ray detection signal after correction by removing a time delay from each X-ray detection signal by recursive calculation processing as an impulse response composed of a plurality of exponential functions ( 10).

That is, in the case of the FPD 2, as shown in Fig. 5, the X-ray detection signal at each time includes a signal corresponding to past X-ray irradiation as a time delay (diagonal portion). This time delay is removed by the time delay removal unit 10 to be a corrected X-ray detection signal without time delay, and an X-ray image is generated by the detection signal processing unit 4 based on the corrected X-ray detection signal. do.

Specifically, the time delay removal unit 10 performs a recursive calculation process for removing the time delay from each X-ray detection signal using the following equations A to C. FIG.

Δt: Sampling time interval

     k: subscript representing the kth point in time in the sampled time series

Y _k : the radiation detection signal extracted at the kth sampling time point

X _k : Radiation detection signal after correction removing time delay from Y _k

X _k-1 : X _k before 1

S _{n (k-1)} : S _nk before 1

     exp: exponential function

     N: Number of exponential functions with different time constants constituting the impulse response

     n: subscript representing one of the exponential functions that make up the impulse response

: Strength of exponential function n

: Decay time constant of exponential function n

when k = 0 X ₀ = 0, S _n0 = 0

In other words, the term `` Corresponds to the time delay, the device of the first embodiment is quickly obtained by a simple ignition equation in which the X-ray detection signal X _k after correction, which has eliminated the time delay, is represented by equations A to C.

In addition, the apparatus of the first embodiment stores in advance a correspondence relationship between an impulse response coefficient and an X-ray irradiation dose which define a condition related to an impulse response in the recursive computation in the time delay elimination section 10. The correspondence relationship between the impulse response coefficient and the X-ray irradiation dose stored in the coefficient-dose-correspondence memory unit (response coefficient-dose-correspondence relationship storage means) 11 and the response coefficient-dose-correspondence relationship memory unit 11 Therefore, an impulse response coefficient setting unit (impulse response coefficient setting means) 12 for setting an impulse response coefficient suitable for the X-ray irradiation dose to the inspected object is provided. Then, the time delay removing unit 10 performs a recursive calculation process according to the impulse response coefficient set by the impulse response coefficient setting unit 12 to remove the time delay included in each X-ray detection signal, It has the characteristic feature of constructing X-ray detection signal after correction.

The response coefficient and dose correspondence relationship memory section 11 stores in advance a correspondence relationship between the impulse response coefficient and the X-ray irradiation dose as a correspondence relationship between the impulse response coefficient and the X-ray irradiation dose. In the case of the first embodiment, the correspondence between the intensity of the exponential function as the impulse response coefficient and the X-ray irradiation dose stored in the response coefficient / dose correspondence memory 11 is the same irradiation time and the X-ray irradiation dose is stepwise. The attenuation characteristics of the X-ray detection signals of some X-ray images actually photographed under different conditions are measured and obtained. Specifically, for example, the intensity of the exponential function suitable for each X-ray image is obtained based on some images (radiation data) of which the amount of X-ray irradiation differs step by step. As shown in FIG. 6, the strength of the obtained exponential function And its strength The X-ray irradiation dose W at the time of photographing the underlying X-ray image is plotted as an X-ray irradiation dose, and the vertical axis is plotted as the intensity of the exponential function. In addition, a function expression representing a curve connecting the plotted points is obtained as the correspondence between the intensity of the exponential function and the X-ray irradiation dose. Then, the correspondence between the strength of the calculated exponential function and the X-ray irradiation dose is stored in advance in the response coefficient and dose correspondence relationship memory unit 11 in the function equation. Strength of exponential function Is proportional to the logarithm of the X-ray radiation dose W.

Moreover, in order to make the same irradiation time at the time of X-ray imaging, the operation part 7 always sets the width | variety of an X-ray pulse constantly. In order to change the X-ray irradiation dose step by step, the operation unit 7 changes the tube current mA of the X-ray tube 1 step by step. At this time, the X-ray irradiation dose is changed at an appropriate interval with respect to the range of possibility of use (between the maximum irradiation dose and the minimum irradiation dose). In the measurement of the attenuation characteristic of the X-ray detection signal of the X-ray image, the X-ray image is photographed at a constant irradiation time (for example, 10 seconds) using the phantom as the subject M. The derivation and storage of the correspondence relationship between the intensity of the exponential function and the X-ray irradiation dose are performed at the time of installation (fixing) or at regular adjustment.

Thus, in the case of the apparatus of the first embodiment, the correspondence relationship between the intensity of the exponential function as the impulse response coefficient and the X-ray irradiation dose is the same irradiation time, and the multiple X-rays actually photographed under the different conditions step by step. Since it is derived based on an image, i.e., an actual image, the intensity of the exponential function and the X-ray irradiation dose can be accurately matched.

In addition, the intensity of the exponential function as the impulse response coefficient shown in FIG. And the correspondence relationship between the X and the X-ray irradiation dose W can be expressed by the following simple function.

only, : Strength of exponential function

    W: radiation dose

    Q: slope of the approximate line representing the relationship between the strength of the exponential function and the radiation dose

    q: Intercept of the approximation line indicating the relationship between the intensity of the exponential function and the radiation dose

In addition, the inclination Q of the approximation straight line and the intercept q of the approximation straight line can be obtained as follows. That is, as shown in FIG. 7, the horizontal axis is scaled to logW, and the vertical axis is Draw a scale with The slope of the straight line when the graph is straightened is the slope Q of the approximated straight line, and the coordinate on the longitudinal axis of the point where the straight line intersects the vertical axis is the intercept q of the approximated straight line.

Therefore, in the case of the apparatus of the first embodiment, the strength of the exponential function as the impulse response coefficient And the correspondence relationship between the X-ray irradiation dose W and the response coefficient and the dose correspondence relationship memory unit 11 can be easily stored in the above simple function.

In addition, in the apparatus of the first embodiment, there are a plurality of exponential functions constituting the impulse response, and the correspondence relationship between the intensity of the exponential function as the impulse response coefficient and the X-ray irradiation dose is stored for each exponential function. The number of concrete exponential functions is two or three. In other words, one of the above functions is stored for each exponential function constituting the impulse response coefficient, and the slope Q of the approximating straight line and the intercept q of the approximating straight line take appropriate values between the respective functional equations.

Thus, since the impulse response is composed of a plurality of exponential functions, the impulse response is more accurate. In addition, since the correspondence between the intensity of the exponential function as the impulse response coefficient and the X-ray irradiation dose is stored for each exponential function, the strength of each exponential function can be appropriately set. As a result, the time delay included in each X-ray detection signal is more accurately removed.

On the other hand, the impulse response coefficient setting unit 12 is set as follows. That is, during X-ray imaging, for example, the X-ray irradiation dose is calculated from the width of the X-ray pulse and the tube current (mA) set by the operation unit 7, and then the calculated X-ray irradiation dose is calculated. Assign to the formula of. Impulse response as the intensity of the exponential function in the recursive calculation processing performed by the time delay elimination unit 10 after obtaining the intensity of the exponential function appropriate for the X-ray irradiation amount in the X-ray image being executed. The coefficient setting unit 12 sets.

On the other hand, the time delay removing unit 10 performs recursive calculation processing according to the impulse response coefficient set by the impulse response coefficient setting unit 12 to remove the time delay included in each X-ray detection signal.

Moreover, as the apparatus of the first embodiment, the A / D converter 3, the detection signal processing section 4, the irradiation control section 6, the time delay removing section 10, the response coefficient and dose correspondence relation memory section 11 are provided. Each part, such as an impulse response coefficient setting part 12, performs control and processing according to the instruction input from the operation part 7 or the various commands sent from the main control part 13 in accordance with the progress of data or X-ray imaging. .

Next, the case where X-ray imaging is performed using the apparatus of the above-described first embodiment will be described in detail with reference to the drawings. 8 is a flowchart showing a procedure of X-ray imaging by the apparatus of the first embodiment. In addition, the response coefficient and dose correspondence relation memory unit 11 has an intensity of an exponential function as an impulse response coefficient. It is assumed that a function expression indicating a correspondence relationship between the X and the X-ray irradiation dose W has already been stored, and the inspected object M is placed on a large board and set at the photographing position.

[Step S1] The operation unit 7 is operated to input an imaging condition in which the operator includes the X-ray irradiation dose.

[Step S2] The impulse response coefficient setting unit 12 substitutes the X-ray irradiation dose set by the operator into a function formula stored in the response coefficient and dose-correspondence relationship memory unit 11, and the X-ray irradiation dose set by the operator. Exponential strength Obtain and set. In the case of the first embodiment, since the number of exponential functions constituting the impulse response is plural, only the number of exponential functions is derived and set.

[Step S3] An X-ray detection signal for one X-ray image before X-ray irradiation from the FPD 2 at the sampling time interval Δt (= 1/30 second) in the state of no X-ray irradiation. Extraction of Y _k starts, and the extracted X-ray detection signal is stored in the detection signal memory section 8.

[Step S4] X-rays for one X-ray image by the A / D converter 3 at a sampling time interval Δt in parallel with irradiation of the X-rays to the subject M under continuous or intermittent operation by setting the operator. Extraction of the detection signal Y _k and storage in the detection signal memory section 8 are continued.

[Step S5] When the X-ray irradiation ends, the process proceeds to the next step S6. If the X-ray irradiation does not end, the process returns to step S4.

[Step S6] The X-ray detection signal Y _k for the one X-ray image collected in one sampling from the detection signal memory section 8 is read.

[Step S7] after correction to remove the time delay minutes a recursive computation process by the time delay removing (10) the formula A ~ C and, from the respective X-ray detection signals Y _k X-ray detection signal X _k, that is, the pixel Find the value.

In the first embodiment, the impulse response coefficient setting unit 12 sets an appropriate value according to the X-ray irradiation dose input by the operator with respect to the strength of the exponential function of the impulse response coefficient. Number N of exponential functions or time constant of exponential function Is determined in advance regardless of the X-ray irradiation dose, and an appropriate constant value is set.

[Step S8] The detection signal processing unit 4 creates an X-ray image based on the X-ray detection signal X _k after correction of one sampling (for one X-ray image).

[Step S9] The created X-ray image is displayed on the image monitor 5.

[Step S10] If the unprocessed X-ray detection signal _Yk remains in the detection signal memory section 8, the process returns to Step S6. If the unprocessed X-ray detection signal _Yk does not remain, X-ray imaging is terminated.

Further, in the apparatus of the first embodiment, the time delay elimination section 10 for the X-ray image detection signal Y _k for one X-ray image is calculated and the detection signal processing section 4 calculates the X-ray detection signal X _k after correction. The X-ray image is created at a sampling time interval Δt (= 1/30 second). That is, one-second X-ray images are sequentially created at a speed of about 30 sheets, and the generated X-ray images are continuously displayed to display moving images of the X-ray images.

Next, the process of the recursive calculation processing by the time delay removing unit 10 of step S7 in FIG. 8 will be described using the flowchart of FIG. 9.

9 is a flowchart showing a recursive computation processing process for eliminating time delay by the apparatus of the first embodiment.

[Step R1] k = 0 is set, and both X ₀ = 0 in formula A and S _n0 = 0 in formula C are all set as initial values before X-ray irradiation. When the number of exponential functions is three (N = 3), S ₁₀ , S ₂₀ , and S ₃₀ are all set to O.

[Step R2] In formulas A and C, k = 1 is set. According to the formula C, i.e., S _n1 = X _O + exp (T _n ) · S _n0 , S ₁₁ , S ₂₁ , S ₃₁ are obtained, and the obtained S ₁₁ , S ₂₁ , S ₃₁ and the X-ray detection signal Y _k are obtained. Substituting the equation A, the corrected X-ray detection signal is calculated.

[Step R3] After increasing k by 1 (k = k + 1) in Equations A and C, X _k-1 before 1 time point is substituted into Equation C to obtain S _1k , S _2k , and S _3k . The obtained X-ray detection signal X _k is calculated by substituting S _1k , S _2k , S _3k and the X-ray detection signal Y _k into Equation A.

[Step R4] If there is an unprocessed X-ray detection signal Y _k , the process returns to Step R3. If there is no unprocessed X-ray detection signal Y _k , the process proceeds to the next step R5.

[Step R5] After the correction of one sampling amount (for one X-ray image), the removal X-ray detection signal X _k is calculated, and the recursive calculation processing for one shot is finished.

As described above, according to the apparatus of the first embodiment, in the time delay removing unit 10, the time delay removal is performed in the state where the strength of the exponential function as the impulse response coefficient is set to the X-ray irradiation dose to the subject M. Since the recursive arithmetic processing is performed, the time delay included in each X-ray detection signal is accurately removed. Therefore, according to the apparatus of the first embodiment, it is possible to accurately eliminate the time delay of the X-ray detection signal due to the FPD 2 from the X-ray detection signal extracted from the FPD 2.

Second embodiment

In the X-ray fluoroscopy apparatus of the second embodiment, the response coefficient / dose-correspondence relationship memory section 11 has an intensity of an exponential function as an impulse response coefficient. And the table memory for storing the correspondence relationship between the X and the X-ray irradiation dose W in the form of a table, not a function expression, and thus are the same as those of the apparatus of the first embodiment. Therefore, only different points are described, and description of common points is omitted.

That is, in the case of the apparatus of the second embodiment, the strength of the exponential function as the impulse response coefficient And the correspondence relationship between the X-ray irradiation dose W and the X-ray irradiation dose W are stored in a table memory in a table format. The impulse response coefficient setting unit 12 compares the X-ray irradiation dose input by the operator with a list stored in the response coefficient-dose-correspondence relationship memory section 11, and an index suitable for the X-ray irradiation dose input by the operator. Strength of function Read it and set it.

Also in the case of the apparatus of the second embodiment, the time delay removing unit 10 is also used for removing the time delay in a state in which the strength of the exponential function as an impulse response coefficient appropriate for the X-ray irradiation dose to the subject M is set. Since the recursive computation process is performed, the time delay included in each X-ray detection signal is accurately removed. Therefore, according to the apparatus of the second embodiment, it is possible to accurately eliminate the time delay of the X-ray detection signal due to the FPD 2 from the X-ray detection signal extracted from the FPD 2.

The present invention is not limited to the above embodiment and can be modified as follows.

(1) In each device described above, the response coefficient / dose correspondence memory unit 11 stores the correspondence between the intensity of the exponential function as the impulse response coefficient and the X-ray irradiation dose, but as a pulse response coefficient. Time constant of exponential function And the correspondence relationship between the X-ray irradiation dose and the correspondence relationship between the number N of the exponential function as the pulse response coefficient and the X-ray irradiation dose.

(2) Although the radiation detecting means was FPD in each of the above described apparatuses, the present invention can be applied to an apparatus having a configuration using radiation detecting means which causes time delay of X-ray detection signals other than FPD.

(3) Although each of the above-described embodiments of the apparatus was an X-ray perspective imaging apparatus, the present invention can also be applied to other than an X-ray perspective imaging apparatus such as an X-ray CT apparatus.

(4) Although the apparatus of each Example mentioned above was a medical apparatus, this invention is applicable not only to medical use but also to industrial apparatuses, such as a non-destructive inspection apparatus.

(5) Although each Example apparatus mentioned above was an apparatus which uses X-rays as radiation, this invention is applicable to the apparatus which uses radiation other than X-rays, not only X-rays.

In the case of the radiographic image capturing apparatus of the present invention, when the time delay is removed from the radiation detection signal by the recursive calculation processing by the time delay removing means and the corrected radiation detection signal is calculated, the recursive calculation processing for the time delay removal is performed. The response coefficient / dose correspondence storage means memorizes in advance the correspondence relationship between the impulse response coefficient and the radiation dose, which prescribes the conditions relating to the impulse response in the system, and the correspondence relationship between the impulse response coefficient and the radiation dose. Therefore, the impulse response coefficient setting means sets an impulse response coefficient suitable for the radiation to the inspected object, and a recursive computation process for removing time delay is performed while the impulse response coefficient is set for the radiation dose to the inspected object. Accurately remove the time delay included in each radiation detection signal.

Therefore, according to the radiation imaging apparatus of the present invention, it is possible to accurately remove the time delay of the radiation detection signal due to the radiation detection means from the radiation detection signal extracted from the radiation detection means represented by, for example, FPD.

1 is a block diagram showing the overall configuration of an X-ray perspective imaging apparatus of the first embodiment;

2 is a plan view showing the configuration of an FPD used in the apparatus of the first embodiment;

3 is a cross sectional view of an FPD used in the apparatus of the first embodiment;

4 is a schematic diagram showing a sampling situation of an X-ray detection signal at the time of performing X-ray imaging by the apparatus of the first embodiment;

5 is a signal waveform diagram showing a time delay situation in an X-ray detection signal;

6 is a graph showing a correspondence relationship between the intensity of an exponential function as an impulse response coefficient and an X-ray irradiation dose in the first embodiment;

FIG. 7 is a graph showing an approximation straight line corresponding relationship between the intensity of the exponential function as the impulse response coefficient and the X-ray irradiation dose in the first embodiment;

8 is a flowchart showing a procedure of X-ray imaging by the apparatus of the first embodiment;

9 is a flowchart showing a recursive computation processing process for eliminating time delay by the apparatus of the first embodiment;

Fig. 10 is a schematic diagram showing the storage contents of the table memory for the response coefficient / dose-correspondence relationship memory section of the apparatus of the second embodiment.

Claims (14)

Radiation irradiation means for irradiating radiation to the inspected object, radiation detecting means for detecting radiation transmitted through the inspected object, and signal sampling means for extracting a radiation detection signal from the radiation detecting means at a predetermined sampling time interval; A radiation image pickup device configured to obtain a radiographic image on the basis of a radiation detection signal output at a sampling time interval from a radiation detection means in response to irradiation to a subject under test, Time delay that is included in each radiation detection signal extracted at sampling time intervals by impulse response composed of a plurality of exponential functions with different singular or attenuation time constants and is removed from each radiation detection signal by recursive computation. Removal means; Response coefficient / dose correspondence storage means for storing in advance the correspondence between the impulse response coefficient and the irradiation dose in which the condition related to the impulse response is determined in the recursive computation processing in the time delay removing means; Impulse response coefficient setting means for setting an impulse response coefficient corresponding to the irradiation dose to the subject under test according to the correspondence relationship between the impulse response coefficient stored in the response coefficient and the dose correspondence relationship storage means and the radiation dose; The time delay elimination means performs recursive calculation processing according to the impulse response coefficient set by the impulse response coefficient setting means, removes the time delay included in each radiation detection signal, and obtains a post-correction radiation detection signal. Device. The method of claim 1, The response coefficient and dose correspondence relationship storage means is a correspondence relationship between the impulse response coefficient and the radiation irradiation means, Correlation of Exponential Function as Impulse Response Coefficient with Irradiation Dose, Correlation between Exponential Function's Attenuation Time Constant and Irradiation Dose as Impulse Response Coefficient, And at least one of a correspondence relationship between the number of exponential functions as an impulse response coefficient and the radiation dose in advance. The method of claim 1, The time delay removing means is a recursive calculation process for removing the time delay from the radiation detection signal Equation A ~ C, Δt: Sampling time interval      k: subscript representing the kth point in time in the sampled time series Y _k : the radiation detection signal extracted at the kth sampling time point X _k : Radiation detection signal after correction removing time delay from Y _k X _k-1 : X _k before 1 S _{n (k-1)} : S _nk before 1      exp: exponential function       N: Number of exponential functions with different time constants constituting the impulse response       n: subscript representing one of the exponential functions that make up the impulse response : Strength of exponential function n : Decay time constant of exponential function n when k = 0 X ₀ = 0, S _n0 = 0 A radiation imaging apparatus configured to be performed by The method of claim 1, As the impulse response coefficient, including the strength of the exponential function, A radiation image pickup apparatus, wherein a correspondence relationship between the intensity of an exponential function as an impulse response coefficient and a radiation dose is derived based on a plurality of radiation data actually photographed at different conditions in stages at the same irradiation time. The method of claim 1, As the impulse response coefficient, including the strength of the exponential function, And a plurality of exponential functions constituting the impulse response, and the correspondence relationship between the intensity of the exponential function as the impulse response coefficient and the irradiation dose is stored for each exponential function. The method of claim 1, As the impulse response coefficient, including the strength of the exponential function, The correspondence between the intensity of the exponential function as the impulse response coefficient and the radiation dose, only, : Strength of exponential function      W: radiation dose      Q: slope of the approximate line representing the relationship between the strength of the exponential function and the radiation dose      q: A radiographic image capturing apparatus represented by a function formula that is an intercept of an approximation line indicating the relationship between the intensity of an exponential function and the radiation dose. The method of claim 1, And the response coefficient and dose correspondence relationship storing means is a table memory for storing the correspondence relationship between the impulse response coefficient and the irradiation dose in a table format. In the radiation detection signal processing method of irradiating an object to be examined and extracting the detected radiation detection signal at a predetermined sampling time interval, and performing signal processing to obtain a radiographic image based on the radiation detection signal output at the sampling time interval, Removing the time delay included in each radiation detection signal extracted at a sampling time interval from each radiation detection signal by recursive calculation processing as an impulse response composed of a plurality of exponential functions having different singular or attenuation time constants; Before the removing step, the conditions related to the impulse response are defined in the recursive calculation process, and the impulse corresponding to the irradiation dose to the inspected object is determined according to the correspondence relationship between the previously stored impulse response coefficient and the irradiation dose. Setting a response coefficient; And a step of obtaining a post-correction radiation detection signal by performing a recursive calculation process in the removing step to remove the time delay included in each radiation detection signal in accordance with the impulse response coefficient set in the setting step. Detection signal processing method. The method of claim 8, Recursive computations to remove time delays from radiation detection signals Δt: Sampling time interval      k: subscript representing the kth point in time in the sampled time series Y _k : the radiation detection signal extracted at the kth sampling time point X _k : Radiation detection signal after correction removing time delay from Y _k X _k-1 : X _k before 1 S _{n (k-1)} : S _nk before 1      exp: exponential function       N: Number of exponential functions with different time constants constituting the impulse response       n: subscript representing one of the exponential functions that make up the impulse response : Strength of exponential function n : Decay time constant of exponential function n when k = 0 X ₀ = 0, S _n0 = 0 The radiation detection signal processing method performed by the. The method of claim 8, As the impulse response coefficient, including the strength of the exponential function, A correspondence relationship between the intensity of an exponential function as an impulse response coefficient and the radiation dose is detected based on a plurality of radiation data actually photographed at the same irradiation time and in different stages of radiation dose. The method of claim 8, As the impulse response coefficient, including the strength of the exponential function, The correspondence between the intensity of the exponential function as the impulse response coefficient and the radiation dose, only, : Strength of exponential function     W: radiation dose     Q: slope of the approximate line representing the relationship between the strength of the exponential function and the radiation dose      q: The radiation detection signal processing method represented by the functional formula which becomes an intercept of the approximation line which shows the relationship between the intensity | strength of an exponential function, and a radiation dose. The method of claim 8, A radiation detection signal processing method which stores the correspondence between the impulse response coefficient and the radiation dose in a table memory in a table format. The method of claim 8, The method is: And a step of storing in advance the corresponding relationship between the impulse response coefficient and the radiation dose. The method of claim 13, The storing step is carried out at the time of installation of the apparatus or at regular adjustment.